Parimal has done 1/4th of a job in 10 days, Salim completes the rest of the job in 20 days. In how many days can they together do the job?

Let total work to be done = 80 units

Work done by Parimal in 10 days = $$\frac{1}{4} \times 80 = 20$$ units

Parimal's efficiency = $$\frac{20}{10} = 2$$ units/day

Remaining work = 80 - 20 = 60 units

Salim completes 60 units in 20 days

=> Salim's efficiency = $$\frac{60}{20} = 3$$ units/day

(Parimal + Salim)'s 1 day's work = 2 + 3 = 5 units/day

$$\therefore$$ Time taken by them together to do the job = $$\frac{80}{5} = 16$$ days

=> Ans - (D)